Steering control system

Abstract

A steering control system for controlling turning of steered road wheels of a motor vehicle in accordance with steering of a steering wheel, comprises a steering angle sensor that detects a steering angle by which the steering wheel is turned; an actuator that turns the steered road wheels when operated; a vehicle operation condition sensor that detects an operation condition of the motor vehicle; a target value determining section that determines a steered angle target value of the steered road wheels in accordance with the steering angle detected by the steering angle sensor and the vehicle operation condition detected by the vehicle operation condition sensor; and an actuator drive circuit that drives the actuator in accordance with the steered angle target value.

1 . A steering control system for controlling a turning movement of steered road wheels of a motor vehicle in accordance with a steering movement of a steering wheel, comprising: 
 a steering angle sensor that detects a steering angle by which the steering wheel is turned;    an actuator that turns the steered road wheels when operated;    a vehicle operation condition sensor that detects an operation condition of the motor vehicle;    a target value determining section that determines a steered angle target value of the steered road wheels in accordance with the steering angle detected by the steering angle sensor and the vehicle operation condition detected by the vehicle operation condition sensor; and    an actuator drive circuit that drives the actuator in accordance with the steered angle target value.    
   
   
       2 . A steering control system as claimed in  claim 1 , further comprising a steered angle sensor that detects a steered angle of the steered road wheels, the target value determining section determining the steered angle target value of the steered road wheels in accordance with the steering angle detected by the steering angle sensor and the steered angle detected by the steered angle sensor.  
   
   
       3 . A steering control system as claimed in  claim 1 , further comprising a back-up steering mechanism that is arranged between the steering wheel and the steered road wheels and operatively independent from the actuator, the back-up steering mechanism functioning to turn the steered road wheels in accordance with the turning of the steering wheel.  
   
   
       4 . A steering control system as claimed in  claim 3 , further comprising: 
 an input shaft through which the steering wheel and the back-up steering mechanism are connected; and    an output shaft through which the back-up steering mechanism and the steered road wheels are connected.    
   
   
       5 . A steering control system as claimed in  claim 4 , in which the back-up steering mechanism comprises: 
 a planetary gear unit having an input part connected to the input shaft and an output part connected to the output shaft; and    an operation mechanism by which rotation speed ratio between the input part and the output part is varied.    
   
   
       6 . A steering control system as claimed in  claim 5 , further comprising an abnormal condition sensing means that detects an abnormal condition of the steering control system, and in which when the abnormal condition sensor senses an abnormal condition, a relative rotation between the input and output parts of the planetary gear unit is restricted.  
   
   
       7 . A steering control system as claimed in  claim 5 , in which the operation mechanism comprises: 
 a worm gear formed on a ring gear of the planetary gear unit;    a worm shaft meshed with the worm gear;    an electric motor that drives the worm gear; and    an electric motor drive circuit that controls operation of the electric motor in accordance with the steered angle target value determined by the target value determining section.    
   
   
       8 . A steering control system as claimed in  claim 7 , in which the operation mechanism stops rotation of the electric motor when the abnormal condition sensing means detects the abnormal condition of the steering control system.  
   
   
       9 . A steering control system as claimed in  claim 7 , further comprising a torque sensor that is arranged between the back-up steering mechanism and the steered road wheels to detect a steering torque, the operation mechanism controlling the electric motor in accordance with the steering torque detected by the torque sensor.  
   
   
       10 . A steering control system as claimed in  claim 7 , further comprising a rotation angle sensor that senses a rotation angle of the electric motor, the operating mechanism controlling the electric motor in accordance with the steering angle detected by the steering angle sensor and the rotation angle detected by the rotation angle sensor.  
   
   
       11 . A steering control system as claimed in  claim 3 , further comprising a torque sensor that is arranged between the back-up steering mechanism and the steered road wheels to detect a steering torque, the actuator drive circuit controlling the actuator in accordance with the steering torque detected by the torque sensor.  
   
   
       12 . A steering control system as claimed in  claim 3 , further comprising: 
 a torsion bar arranged between the back-up steering mechanism and the steered road wheels;    a real steering angle sensor that is arranged between the back-up steering mechanism and the torsion bar to detect a real steering angle;    a steered angle sensor that detects a steered angle by which the steered road wheels are turned; and    a control section that derives a twisted degree of the torsion bar based on both the real steering angle and steered angle and derives a steering torque from the twisted degree.    
   
   
       13 . A steering control system as claimed in  claim 12 , further comprising a yaw rate sensor for sensing a yaw rate of the vehicle, the actuator drive circuit driving the actuator in accordance with the yaw rate detected by the yaw rate sensor.  
   
   
       14 . A steering control system of a steer-by-wire type steering device, the steering device including an electric motor for turning steered road wheels of a motor vehicle, and a torsion bar operatively interposed between a steering wheel and the steered road wheels, 
 the steering control system comprising:    a vehicle speed sensor that detects a running speed of the vehicle;    a steering angle sensor that detects a steering angle by which a steering wheel of the vehicle is turned;    a steered angle sensor that detects a steered angle of steered road wheels of the vehicle;    a torque sensor that detects a torque applied to the torsion bar;    a first means that, by processing the running speed of the vehicle detected by the vehicle speed sensor and the steering angle detected by the steering angle sensor, outputs a target steered angle signal that represents a target value of steered angle of steered road wheels of the vehicle;    a second means that, by processing the target steered angle signal from the first means and the steered angle detected by the steered angle sensor, outputs a corrected steered angle signal that represents a corrected value of the steered angle of the steered road wheels of the vehicle, the corrected steered angle signal being fed to the electric motor for controlling the turning of the steered road wheels; and    a third means that, by processing the torque detected by the torque sensor, produces a steering reaction force that is to be applied to the steering wheel.    
   
   
       15 . A steering control system as claimed in  claim 14 , further comprising a yaw rate sensor that detects a yaw rate of the vehicle, the first means processing the yaw rate for outputting the target steered angle signal.